The He(I) photoelectron spectrum of bis(pentadienyl) iron: A comparison with the ferrocene spectrum

The He(I) photoelectron (PE) spectrum of bis(pentadienyl)iron (1) is reported. An interpretation is presented based on correlations with the PE spectra of methyl derivatives and on INDO-type calculations. It is possible to assign the PE bands of 1 to individual MO's by taking into account the differing Koopmans' defects in the framework of the Green's-function technique. It is shown that the PE spectrum of 1 cannot be correlated directly with that of ferrocene (2), although the two spectra appear very similar. The differences between 1 and 2 are discussed.     

He(I) and He(II) photoelectron spectra of glycine and related molecules

Photoelectron spectra obtained by He(I) and He(II) excitation of glycine, sarcosine and glycine methyl ester are presented. The p-type bands in the He(I) spectrum of glycine are interpreted in terms of localized molecular orbitals; the C 2s bands are identified in the He(II) spectrum. He(I) spectra of some N-acetylamino acids and of a variety of α-and ω-substituted amino acids are also reported.     

He(I) and He(II) photoelectron spectra of iron tetracarbonyl-olefin complexes

The He(I) and He(II) photoelectron spectra of a series of iron tetracarbonyl—olefin complexes (olefin = acrolein, crotonaldehyde, methyl acrylate, acrylic acid, dimethyl maleate and some dihalogenated ethylenes) are reported. Assignments are proposed, based on differences in intensity between the He(I) and He(II) spectra, in comparison with related compounds and the results of extended CNDO calculations. The electronic structure of the coordinated olefins is discussed.     

He(I) and He(II) photoelectron spectra of some substituted ethylenes

The He(I) and He(II) photoelectron spectra of acrolein, acrylic acid, methyl acrylate, vinyl acetate, acrylamide and some of their methyl-substituted analogues are reported. Detailed assignments are proposed, mainly based on differences in intensity between the He(I) and He(II) spectra, on sum rule considerations and on the results of modified CNDO/S calculations.The assignment criteria are critically evaluated.     

On the He(I) and Ne(I) photoelectron spectra of OCS

The He(I) (58.43 nm) and Ne(I) (73.59–74.37 nm) photoelectron spectra of carbonyl sulphide have been reinvestigated at an improved resolution and a high signal-to-noise ratio; deconvolution of the data was carried out to aid interpretation of the spectra. Improved values are deduced for the vibrational wavenumbers and the ionization energies. The spin—orbit components of the Ã²Π II level are well resolved and a value of 135 cm^?1 (17 ± 5 meV) is proposed for the splitting. Perturbations in the relative intensities are observed in the Ne(I) spectrum; they suggest that the autoionizing Rydberg state located around 73.7 nm is excited by the 73.59 nm Ne(I) line and contributes to populate, with different probabilities, the ionic levels of lower energy, and particularly the X?²Π state.     

Ultraviolet photoelectron spectra of selenium and tellurium

He(Iα)He(IIα) spectra are presented for selenium and tellurium both in the gas phase and as condensed solids. Analysis of the He(IIα) and He(Iα configuration-interaction effects are less important than was previously thought. Measurements of He(IIα)/He(Iα) photoionization cross-section ratiThe spectra of the condensed solids indicate that while Te rapidly forms a polycrystalline solid, selenium condenses initially as an amorphous solid wi changes rapidly to give the normal room-temperature spectrum of amorphous selenium. Comparison of the stable amorphous spectrum with that of the polyme contains a large number of cyclic polymers.     

He(II) photoelectron spectra of the Group IVB tetrachlorides

He(II) photoelectron spectra of the Group IVB tetrachlorides MCl₄ (M = C, Si, Ge, Sn) are reported and compared with He(I) data. The discussion concentrates on the spectral intensity patterns and the nature of the additional structure revealed in the He(II) spectra.     

Photoelectron spectroscopic studies of the monomers and dimers of acetic and trifluoracetic acids

Comparison of the He(I) and He(II) photoelectron spectra of acetic and trifluoracetic acids has clarified the assignments of their p-based ionization potentials. The He(I) spectra of the gas-phase homodimer of each molecule have been observed using a high-pressure nozzle inlet system operating at room temperature. Spectrum-stripping of the monomer—dimer mixed-spectra gives dimer spectra which are interpreted with the aid of molecular orbital calculations. Appropriate mixtures of the two acids have been analyzed to obtain the He(I) spectrum of the 1:1 heterodimer. Assignments of the three dimer spectra indicate that the inductive influences of the methyl and trifluoromethyl groups are transmitted across the hydrogen-bond bridges.     

Fine structure in the He(I)/He(II) photoelectron spectra of the metal valence (d) shells of the group IIB dihalides

The He(I) and He(II) photoelectron spectra of the group IIB dihalides (except the difluorides) are reported. Emphasis is laid on the metal valence d-shell ionizations. These are discussed in terms of He(I)/He(II) relative intensity changes a ligand-field model. It appears that the observed d-shell structure is the result of a balance between simple field-effects and covalency.     

Theoretical interpretation of photoelectron spectra for transition metal compounds. The He(I) and He(II) spectra of MF2 molecules (M = Co,Ni and Cu)

Calculated vertical ionization energies (VIEs) and relative intensities (RIs) have been used in interpreting He(I) and He(II) photoelectron spectra of MF₂ molecules, M being Co, Ni and Cu. VIEs have been obtained by the Green's function technique applying the semiempirical CNDO-UHF method. Within the framework of the Gelius-Siegbahn model, but utilizing the theoretical atomic cross-sections, the molecular photoionization cross-sections (and the corresponding relative intensities of spectral bands) have been calculated for He(I) and He(II) spectra of MF₂ molecules. A comparison of the theoretical and experimental VIEs and RIs shows that the procedure is useful in ascribing photoemission peaks at particular binding energies of He(I) and He(II) spectra to the set of molecular orbitals.     

Photoionization cross sections: Interpretation of band intensities in He I and He II photoelectron spectra

Relative photoionization cross sections of molecules consisting of atoms from the first three rows of the Periodic Table are computed by a theoretical method developed previously which involves the plane-wave approximation for the photoelectron and the use of semiempirical LCAO-SCF-MO's of the CNDO- or MINDO- type for the initial orbital. The calculated values are compared with experimental photoelectron band intensities obtained by integrating the band areas in He I and He II photoelectron spectra. The observed relative intensity changes of bands in the spectrum in going from He I to He II excitation are attributed to variations in the one- and/or two-centre contributions to the cross sections from the electron density at the atoms and in the bonds, respectively. The analysis of the relative intensities of bands in the He I and He II spectra thus leads to conclusions about the electron density distribution in the initial orbital and about the assignment of the bands.In a qualitative sense, the experimental He I/He II intensity changes are usually correctly predicted by our theoretical method, but there are often considerable quantitative discrepancies between the measured and calculated values which probably arise from the inherent simplifications of our approach.     

Preequilibrium neutron emission in109Ag(3He,xn) and111Cd(p,xn) reactions

Excitation functions of the reactions¹⁰⁹Ag(³He,xn) and¹¹¹Cd(p, xn) have been measured with stacked foil techniques for projectile energies E≦45 MeV and multiplicitiesx≦4 populating ground and spin isomeric states in^112?x In. Preequilibrium (PE) contributions are more pronounced for thep than for the³He entrance channel and for low multiplicitiesx and can be reproduced with the (geometry dependent) hybrid model. The observed isomeric cross section ratios require a reduced population for the high spin state (as compared with the expectation for equilibrated systems) whenever PE emission contributes significantly. Calculations for a full statistical model with a PE decay mode and approximate angular momentum conservation indicate PE neutron emission to be stretched in angular momentum space. For the (p, xn) reactions a more detailed coupling scheme is imperative whereas the (³He,xn) data suggest the competitive PE emission of complex particles.     

He(I) Photoelectron spectroscopy of transient species: fluorothiocyanate (FSCN)

Valence ionisation energies, obtained using He(Iα) photoelectron spectroscopy, of the hitherto unknown and unstable molecule FSCN are presented. Interpretation of the spectra is based on experimental considerations, correspondence with the spectra of related molecules, and the results of Hartree—Fock—Slater calculations using STF basis sets of double-zeta quality. The molecule is shown to exist in the thiocyanate form.     

He(I) photoelectron spectra of bis(β-diketonate)nickel(II) complexes and their mono- and di-thio analogues

The vapor-phase He(I) photoelectron spectra of a series of bis(β-diketonate) nickel(II) complexes and some mono- and di-thio analogues are reported. The spectra are discussed in terms of the metal-ligand bonding present, and the effect on this bond of replacing oxygen donor atoms by sulphur donor atoms.     

UV photoelectron spectra of the indium(I) and thallium(I) cyclopentadienides

Vapour-phase He I and He II photoelectron spectra of the cyclopentadienides of indium(I) and thallium(I) are reported. The discussion concentrates on the implications of the changes in band intensity that are observed on switching from He I to He II excitation, and on the nature of the additional structure revealed in the He II spectra.     

The angular-distribution He(I)/Ne(I) photoelectron spectra of cyclopropane

The angular-distribution photoelectron spectrum of cyclopropane, studied with both He(I) and Ne(I) radiations, indicates negligible change in the asymm     

He(I)/He(II) photoelectron band intensity ratios for simple organic molecules

Band intensifies in the He(I) and HE(II) photoelectron spectra of some simple organic molecules (methanol, methylamine, formaldehyde, acetaldehyde, formic acid, acetic acid, methyl formate, ethylene, butadiene and methyl isothiocyanate) have been measured. The relative band intensity ratios for a number of ionizations from n and π orbitals are presented.     

The He(I) photoelectron spectra of some γ-substituted Co(III) acetylacetonate complexes

The He(I) photoelectron spectra of the complexes of Co(III) with acetylacetone and several derivatives are reported. The ionization potentials of metal-localized d-electrons and ligand π-orbitals are used to probe the extent of metal-to-ligand π-bonding and possible aromatic character in the chelate ring.     

The electronic structure of dinuclear transition-metal complexes containing metal—metal interactions: II. He(I) and He(II) photoelectron spectra of hexacarbonyldi-irondisulfur and related complexes

The He(I) and He(II) photoelectron spectra of a series of Fe₂(CO)₆LL¹-type complexes (L = L¹ = S, (i-propyl)S; L,L¹ = t-but of an all-electron, ab initio SCF MO calculation on Fe₂(CO)₆S₂ and of extended CNDO calculations on related molecules. Assignments given ar He(I)/He(II) intensity differences, and on comparison with related molecules.The coordination of the bridging ligands to the metal centres and the nature of the metal—metal interactions are discussed.     

He (Iα) photoelectron spectra of some higher aromatic perfluoro compounds

He(Iα) excited photoelectron spectra, the inferred ionisation energies, and their assignment, are presented for perfluoro-benzene, -naphthalene, -anthracene, -phenanthrene, -pyrene and -acenaphthylene.